McMullan cautioned that this study can only show that decreased kidney function is associated with less sleep, not that less sleep causes the decline in kidney function. For that, more research is needed, he said.

A connection between disrupted sleep and heart disease has been studied before.

A link between reduced sleep and diminished kidney function might be the result of medical conditions that affect kidney function, such as diabetes and high blood pressure, McMullan said.

The body's natural rhythms, or so-called circadian clock, might also play a role, McMullan said. The kidney is timed to work differently during the night than during the day because the demands on the body are different, he explained.

"Maybe short sleep changes the physiology of the kidney over the daily cycle, and these changes might damage the kidney," McMullan suggested.

As the U.S. population ages and as more people suffer from diabetes and high blood pressure, the number of people with kidney disease will increase, and too little sleep may play a part, he added.

Continued

"We are a sleep-deprived society," McMullan said. "The concern is that sleep deprivation will lead to a decline in kidney function."

He said it's likely the findings would also apply to men, but noted that would need to be studied.

The results of the study are scheduled for presentation Thursday at a meeting of the American Society of Nephrology in San Diego. The data and conclusions should be considered preliminary until published in a peer-reviewed medical journal.

For the study, McMullan's team collected data on more than 4,200 women who took part in the Nurses' Health Study. Over 11 years, the women's kidney function was measured at least twice.

Dr. Kenar Jhaveri, a nephrologist at North Shore-LIJ Health System in Great Neck, N.Y., said the connection between sleep and kidney disease is new to him.

"At this point I would be very cautious about giving advice to patients based on this study," he said. "I certainly wouldn't change any sleep habits."

Jhaveri said seven hours of sleep is good for health. "People who sleep too little or too much are at risk for certain disorders," he added. "In terms of kidney disease, this is something that is going to be interesting in how it pans out."